>Myths and Truths About Sharks

By Maureen Halsema

>Busting the Jaws Impression

>Despite what media and movies may lead us to believe, sharks are not man eaters out to get us. Rather, they are widely diverse with more than 350 species ranging greatly in size, habitats and diet. Shark attacks are few and far between with very few species involved. According to the International Shark Attack File, you are about 45,000 times more likely to be killed in a car accident than you are by a shark attack.

>Now that we've cleared up one myth, let's move on to some other common misconceptions.

>Myth I: Sharks can’t communicate

>Okay, so they may not be speaking our language, but sharks do employ a method of communication that should be easily understood: body language. There are some key behaviors that indicate whether a shark is comfortable with your presence, such as slow, natural swimming patterns, or whether you should take some evasive action.

>"Hunching the back is an absolute sign that this animal is not very happy. It is the equivalent of a dog baring its teeth or the hair on its back rising," said George Burgess, director of the Florida Program for Shark Research. Other signs he noted include lowering the pectoral fins, which are the two wing fins in the front, exaggerated movements, such as "zig-zaggy" swimming, quick turns, or diving down and rubbing their belly against the bottom.

>"These are signs of misdirected behaviors, things we do when we are ill at ease," Burgess said. "For example, a nervous chicken pecks at the ground or a nervous guy on a date might tap his feet or rock his leg. We can see that all around the world in terms of animals, that these behaviors are signals. When it comes to large predators like a shark, it's important to key in on these signals."

>Once you learn to recognize shark signals, what should you do if you encounter a shark exhibiting aggressive behavior?

>"If sharks are encountered, it is best to descend to the seabed or to the protection of rocks, a cliff face, or some other obstacle to interfere with the normal feeding attack pattern. If the diver recognizes an agonistic attack pattern from the shark, he should vacate the area, swimming backwards," writes Dr. Carl Edmonds of North Shore Medical Centre in Australia in his book, Diving and Subaquatic Medicine.

>But if you are in an open-water column, those may not be feasible options. Burgess advises, "If you are descending or ascending in the open no-man's-land of the water column and observe a shark, go back to back with your partner doubling your collective field of view with each of you defending half."

>In the unlikely event of an antagonistic shark encounter, Burgess says, "If sharks aggressively approach you, they do respond to a pop to the nose. But keep in mind, the nose is just north of the mouth and if you miss, you are sticking your hand in its mouth. It's better to use a camera or fin. But this doesn't work repetitively, so take advantage of whatever opportunity you have to get yourself into a safe situation or out of the water."

>Myth II: Yum Yum Yellow

>You may be familiar with the phrase, which is associated with the myth that sharks are more attracted to yellow. In actuality, it's not so much the color yellow itself but that in the water it is a high contrast color. Sharks see contrast particularly well, especially in murky waters, so minimizing brightly colored or patterned equipment may help reduce your level of contrast in the water (Then again, in a search and rescue situation, the high contrast is an essential aid to rescuers trying to spot you in the water). Burgess recommends avoiding wearing items that reflect light, such as shiny jewelry, which could be mistaken for fish scales, and even tucking your dive watch under a wetsuit sleeve.

>In white shark territory, Burgess offers additional color considerations: "I like to wear black as much as possible when I'm in the water; however, in white shark territory, you may want to wear blue clothes rather than black to avoid making an impression that you are of one of their food items."

>Myth III: Sharks are found only in saltwater

>Another common misconception is that the only place to encounter sharks is in saltwater. In fact, some sharks can survive in brackish waters where fresh- and saltwater mix, like in estuaries. In truth, sharks can be found in any body of water that has a route connecting them to the ocean.

>One species particularly known for inhabiting freshwater is the bull shark. "It's a big, aggressive species that can be found in the lower reaches of rivers, estuaries and oftentimes will travel very far upstream. It has been observed to travel as far north as Illinois in the Mississippi River," Burgess said. In northern Australia and southeast Asia there are small freshwater sharks. Stingrays are also common in tropical or subtropical freshwater.

>Myth IV: Electrically charged devices repel sharks

>While some claim that electrically charged devices repel sharks, the shark experts seem to think otherwise. "Not only does the sound of some devices attract them, it may actually spook the sharks to the point of reaction," Burgess said. "Sharks can also sense electromagnetic fields."

>And Edmonds writes, "Many methods of repelling sharks will, given different conditions and different sized animals, result in an alerting or an attraction response in the very animals they are meant to deter. This is certainly the case with some electrical and explosive devices."

>In terms of electrical shark deterrents, Edmonds said, "They were effectively disproven by marine biologists with the intense research [done on shark attack prevention] after World War II." He added they are now being promoted again by commercial groups as deterrents, and in some cases, he notes, when sharks are observed to be attracted to the devices, commercial groups cite user error as the cause.

>Myth V: Diving while menstruating attracts sharks

>There are few reported shark attacks on women, and currently, there is no data to support the belief that menstruating females are at an increased risk for shark attacks.

>"Sharks' extraordinary sensory capabilities are well known. They can detect trace amounts of substances over great distances," said Brian Harper, EMT, DMT and Alert Diver medical editor. "Many species are also known for their curiosity; sharks commonly seek the source of new sensory stimuli in their environment."

>On average, the blood lost during menstruation is small and occurs over several days. Harper elaborated, "The fluid discharged during menstruation is a combination of tissues and secretions from inside the uterus, including mucus from the uterine glands, degraded blood from the capillaries that feed the endometrium and the glandular tissue of the endometrium.

>"Sharks are not known to associate this fluid with feeding opportunities. Although they can certainly detect menstrual discharge, there is little reason to suspect it is attractive to them in the way fresh blood is. It is more likely attractive only in the way any novel sensory stimulus—such as urine, splashing or noises – might be."

>Common Sense and Chance Encounters

>For some, encountering a shark while diving can be a rare and exciting experience. They are intriguing and graceful apex predators. It is important, however, to keep safety your highest priority.

If you observe aggressive behaviors, take the appropriate measures to protect yourself.

If you are diving into an area where sharks are likely to be, scan the water first. You don't want to surprise a shark. In addition, a quieter approach, rather than a big splash may be a less disturbing method.

Be alert and aware of your surroundings.

Stick together in groups, particularly with your dive buddy.

Be respectful.

Avoid making sudden or erratic movements.

Know when to abort a dive.

"In the interest of safety, almost any shark over six feet long is capable of causing some harm to humans, with intention or not," Burgess said. "The three most commonly encountered large species include the great white shark, the bull shark and the tiger shark. All three species grow very large in size, usually consume large prey items and their teeth, through evolution, are designed for shearing. They are worldwide in distribution and frequent in shore waters where humans have invaded their space. Oceanic white tips are found in open ocean, but are a very aggressive species." With any of these sharks, it is advisable to take every precaution and exit the water safely.

>Sharks play an essential role in the ecosystem and it can be a delightful and thrilling experience to encounter one. Just be sure to take precautions and actively pay attention to their body language, because we are the visitors and need to learn their natural behaviors.

>"Common sense is the main thing," Burgess said. "We tend to get immersed in our sport; the more we do, the more comfortable we become. We may become so confident that we skip safety steps or miss the warning signs. The fact is each time we enter the sea, we are entering the wilderness; it's an expedition in some ways similar to a safari. No matter how comfortable you are, you still need to be prepared and aware. Remember, every time you blow bubbles, you truly are immersing yourself in a foreign world."